The present invention relates to a filling method and device.
The invention relates more particularly to a method for filling a liquefied gas tank, notably a cryogenic liquid tank, from a liquefied gas reservoir, notably a cryogenic liquid reservoir, the reservoir being fluidically connected to the tank via a filling pipe, the method using a pressure differential generating member for selectively transferring liquid from the reservoir to the tank, the pressure differential generating member being switchable to an on state or an off state, the filling pipe comprising a liquid flow regulating member positioned downstream of the differential generating member, the flow regulating member being movable between a no-flow position in which the flow of liquid is interrupted and at least one flow position in which the flow of liquid is transferred to the tank at a determined flow rate, the method comprising a step of starting the filling, during which step the flow regulating member is moved from the no-flow position to a flow position and a measurement of a first instantaneous pressure in the filling pipe downstream of the flow regulating member.
More generally, the invention may be applied to the filling of any cryogenic container (mobile or otherwise) from any other cryogenic container (mobile or otherwise).
The increasing demand from users for higher-pressure cryogenic liquid stores or reservoirs has led to the systems that fill these reservoirs being equipped with high-pressure pumps, which means to say pumps operating at pressures of between 24 bar and 40 bar. These same filling systems equipped with high-pressure pumps are called upon to fill low-pressure stores rated for pressures of 2 to 15 bar.
It is therefore necessary to fit the receiving reservoir and/or the filling device with a safety system that prevents the tank from being overfilled or over pressurized which would cause this tank to burst. Because the number of tanks to be filled is markedly higher than the number of filling devices, the safety system preferably applies to the filling devices.
There are various safety systems in existence for avoiding such phenomena.
Thus, one known solution is to equip the filling port of the tank with a pneumatic valve which closes when the pressure in the tank reaches a determined threshold. This solution does, however, have disadvantages which include the need to plan maintenance for this pneumatic valve and a high cost of installing it on all the tanks that require protection.
Another known solution is to provide a calibrated orifice at the tank filling port in order to keep the filling flow rate within safe ranges, typically to a flow rate that the existing safety members of the store can discharge. This solution is also installed on the tanks and penalizes filling time.
Another solution uses a rupture disk or a safety valve on the tank. This type of equipment has to be rated with care. However, this rating may be incompatible with the internal pipes of the tank. In addition, if activated, expelled liquid has to be dealt with in an area that presents no risk to the operators. Finally, rupture disks may be subject to corrosion or mechanical fatigue requiring them to be replaced by a qualified technician.
Another solution is to provide an electric overpressure detection system on the tank (if appropriate via a thermistor at the overflow gauge valve) which, in response, stops the filling pump. However, this solution requires special connectors between each tank and each filling device and, where appropriate, relies on action on the part of the operator.
Another solution (cf. for example WO2005008121A1) consists in measuring the pressure at the tank via a safety hose provided for this purpose so as to stop the pump if a problem occurs. However, this solution requires an additional hose connection and suitable circuitry on the tank.
Another solution detects any potential over consumption of the pump and if appropriate switches it off. However, this solution can be applied only to variable-speed electric pumps and unwanted stoppages may be generated.
Another solution is to provide specific fluidic connections between filling devices and tanks according to determined pressure ranges. This solution imposes obvious constraints in terms of logistics in particular.
The document U.S. Pat. No. 6,212,719 describes a system for automatically stopping a filling pump if the supply hose ruptures using two pressure sensors arranged at the two ends of the transfer hose. Detection of a fall in pressure triggers the stopping of the pump.